In active-matrix displays such as liquid crystal displays or organic electro luminescence (EL) displays, thin film transistors (TFTs) are used in pixel circuits.
For example, a thin film transistor includes a substrate, a gate electrode on the substrate, a gate insulating film over the gate electrode, a semiconductor layer on the gate insulating film, a source electrode and a drain electrode which are electrically connected to the semiconductor layer.
Although silicon is often used for semiconductor layers of thin film transistors, organic thin film transistors whose semiconductor layers are made of organic materials have been in development in recent years. For example, Patent Literature 1 (PTL 1) discloses a conventional organic thin film transistor (PTL 1).